Aircraft gas turbine propulsion engine control systems rely on an accurate measure of engine inlet temperature. Engine inlet temperature (TT2_E) is typically measured by two inlet-mounted temperature probes or one inlet mounted temperature probe with two sensing elements. These probes supply engine inlet temperature data to an engine control, which uses the engine inlet temperature data to, among other things, control engine thrust settings. When conditions conducive to icing exist, these probes are heated to prevent ice accumulation.
In addition to the engine inlet temperature probes, most aircraft are equipped with temperature probes that are used to measure external (e.g., ambient) total air temperature (TAT). These aircraft total air temperature probes are typically mounted on the surface of the aircraft. These probes are also heated to prevent ice accumulation, and are typically integrated into the engine control system to provide a backup temperature measurement in the highly unlikely event that the engine inlet temperature probes or probe heater become unavailable.
Recently, airframe manufacturers have begun looking into ways of accommodating certain non-engine aircraft needs without aircraft TAT probes. Even more recently, certain manufactures have requested that the aircraft TAT probes be removed altogether from the propulsion engine control system. This is because doing so can provide significant benefits. Such benefits include, for example, reduced aircraft recurring costs associated with not installing the TAT probes, the heater, and the associated wiring, reduced aircraft weight, reduced maintenance costs associated with the TAT probes, heater, and associated wiring, and a simplified engine control system design.
Unfortunately, there are also some drawbacks associated with removing the TAT probes. The major drawback is the loss of redundancy that the TAT probes provide as the backup temperature measurement in the highly unlikely event that the engine inlet temperature probes or probe heater become unavailable. This lack of redundancy adversely impacts the postulated Loss of Thrust Control (LOTC) rate associated with engine control systems. LOTC is generally considered the inability to modulate power between idle and 90% of rated thrust for the given conditions, and strategies to cope with the loss of engine inlet temperature measurement often result in an inability to achieve at least 90% thrust while maintaining acceptable operability (surge-free and flameout-free operation with acceptable handling qualities). In particular, the LOTC rate, which must meet certain regulatory requirements (e.g., a rate of 1×10−5), increases significantly on certain engine designs if the TAT probes are not available, which may make the engine control system unable to meet the desired LOTC rate.
One possible solution to allow removal of the TAT probes while still meeting the required LOTC rate is to significantly increase the reliability of other system components to compensate for the LOTC rate increase. Such a solution, however, would require significant component redesigns, resulting in cost increases and schedule impacts.
Hence, there is a need for a system and method to allow the TAT probes to be removed without increasing the LOTC rate, to thereby improve overall system reliability because less aircraft components are used. The present invention addresses at least this need.